Sperm whales were hunted for their valuable whale oil, which was widely used to fuel lamps and make soap

He says, 'Based upon recent discussion with colleagues around the world, I lean towards the theory that ambergris forms in the intestines and passes along with faecal matter, forming an obstruction in the rectum.'

Some think the whale will pass the mass, whereas others believe the obstruction grows so large it eventually fatally ruptures the whale's rectum.

Sperm whales live all over the world, meaning deposits of ambergris could be found floating on any ocean or washed up on most shorelines.

But it is uncommon, found in less than 5% of whale carcasses.

It is thought that pygmy (Kogia breviceps) and dwarf (Kogia sima) sperm whales produce the substance in smaller amounts, as they too have cephalopod-rich diets.

When removed from the whale, it has been described as possessing a strong faecal smell.

But the scent is said to be more pleasant once the mass dries out. At this stage it is often described as musky.

Herman Melville even referred to this curious smell in his novel Moby Dick. He wrote of the terrible odour of a dead whale, from which 'stole a faint stream of perfume'.

Ambrein, an odourless alcohol, is extracted from ambergris and used to make a perfume's scent last longer.

For hundreds of years, perfumers have categorised the quality of ambergris according to its colour, with the finest perfumes made from pure white varieties. Black ambergris is the least valuable because it contains the least ambrein.

Ambergris masses change colour with oxidation, which happens when exposed to the sea and air for long periods of time. Between black and white, the colours range from grey to brown.

Due to accessibility and cost, synthetic chemicals have now replaced ambrein in all but the most expensive perfumes.

Ambergris has been used for more than just perfume, however. Early Arab civilisations named it anbar and used it as incense, an aphrodisiac and medicine to cure many ailments, including those of the brain, heart and senses.

Is ambergris putting whales at risk?

When whaling was widespread, sperm whales were hunted for ambergris and other valuable products, such as oil.

Sabin says, 'Whales are now protected worldwide, but could still be at risk in the future.

'There are ongoing pressures from some countries to reintroduce whaling as a mechanism for population management and control.'

Laws regulating the collection and sale of ambergris vary around the world. In some countries ambergris and all other whale-derived products are prohibited, but elsewhere it is either legal or a grey area.

In the UK and Europe, all living species of whales, dolphins and porpoises are protected by law.

However, the Convention on International Trade in Endangered Species (CITES) considers ambergris a waste product of sperm whales that occurs naturally, making it legal to collect it from the beach or sea.

Sabin states, 'Synthetic alternatives to ambergris do exist and the use of these should be encouraged.

'This would prevent whales being viewed in any way as a resource that humans can exploit.'